Differential head integrated touchdown sensors for hard disk drives

ABSTRACT

A method and system for providing a disk drive is described. The disk drive includes media such as one or more disks, a slider, and a head residing on the slider. The head has an air-bearing surface (ABS), a portion of which contacts the media during touchdown. The head further includes a plurality of touchdown sensors. A first touchdown sensor is proximate to the ABS, while a second touchdown sensor is distal from the ABS. The touchdown sensors are capable of detecting a temperature change of 0.1 degree Celsius or, in some embodiments, smaller.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. patent application Ser. No.12/435,280, entitled “HEAD INTEGRATED TOUCHDOWN SENSOR FOR HARD DISKDRIVES”, filed on the same day as the present application andincorporated herein by reference.

BACKGROUND

Disk drives typically use heads residing on sliders to read from andwrite to the magnetic media. Read and write transducers residing in thehead are flown at a small, controlled spacing above to the magneticmedium during read and write operations. Although generally desired tooperate in close proximity to but not touching the disk, the head mayalso contact the media. This prolonged contact, for example on the orderof tens of microseconds or more, is known as touchdown. For example,heads typically use a thermal actuator that generates heat to controlthe head-media spacing. Heat generated by the thermal actuator causeslocal thermal expansion of the head, which locally reduces the spacingbetween the head and magnetic media. The thermal actuator can be drivento induce sufficient heating for contact between the head and media, ortouchdown. This touchdown is intentional and is generally performed oneach drive during initial drive calibration. Touchdown may also occur atother times during disk drive operation, for example due to changes inenvironmental conditions, operation of the disk drive outside of desiredparameters, or contamination to the head that causes the prolongedcontact described above.

Touchdown is detected in the drive operation as well as in testing.Conventional touchdown detection may be performed using a variety oftechniques. For example, touchdown may be detected through disk slowdown, readout channel noise, strain gauges, and/or acoustic emission.However, no single technique works across all media radii. In additionto detecting touchdown for calibration purposes, it is desirable toaccurately detect touchdown in order to limit contact time between thehead and disk. This is because prolonged contact is generallyundesirable during operation as it may lead to drive failure.

Accordingly, what is needed is a system and method for providingimproved touchdown detection.

BRIEF SUMMARY OF THE INVENTION

The disk drive includes media such as one or more disks, a slider, and ahead residing on the slider. The head has an air-bearing surface (ABS),a portion of which contacts the media during touchdown. The head furtherincludes a plurality of touchdown sensors. A first touchdown sensor isproximate to the ABS, while a second touchdown sensor is distal from theABS. The touchdown sensors are capable of detecting a temperature changeof 0.1 degree Celsius or, in some embodiments, smaller.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a portion of an exemplary embodiment of a diskdrive including a touchdown sensor integrated into the head.

FIG. 2 depicts an exemplary embodiment of a head having a transducerincluding integrated touchdown sensors.

FIG. 3 depicts an exemplary embodiment of a graph depicting temperatureversus heater current.

FIGS. 4-5 depict an exemplary embodiment of a touchdown sensor.

FIG. 6 depicts a block diagram an exemplary embodiment of a system fordetecting touchdown using touchdown sensors integrated into a head.

FIG. 7 depicts an exemplary embodiment of a method for detectingtouchdown using touchdown sensors integrated into a head.

FIG. 8 depicts another exemplary embodiment of a method for detectingtouchdown using touchdown sensors integrated into a head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagram of a portion of an exemplary embodiment of a diskdrive 50. For simplicity, components are omitted. In addition, forclarity, FIG. 1 is not drawn to scale. The disk drive 50 includes amedia 60 and a slider 70. On the slider 70 resides head 100, whichincludes integrated touchdown sensors 150 and 160. Each of the touchdownsensors 150 and 160 is a thermal sensor and, in one embodiment, is athermistor.

The touchdown sensor 150 in combination with the touchdown sensor 160detects touchdown based upon the temperature of the head 100. The diskdrive 50 is shown at touchdown. Consequently, the head 100 contacts themedia 60 in a region of the ABS termed a touchdown region. Frictionalheating due to contact between the media 60 and head 100 raises thelocal temperature of the head 100 in the region proximate to wheretouchdown occurs. The touchdown sensor 150 is located in this touchdownregion. Thus, the touchdown sensor 150 is able to detect a localtemperature rise. This local temperature rise may persist due torelatively prolonged contact (for example in the tens of microsecondregime, or more) between the head 100 and disk 60 during touchdown.

In contrast, the touchdown sensor 160 is located distal from the portionof the ABS that is in contact with the media 60. The touchdown sensor160 is thus substantially unaffected by the local temperature rise dueto frictional heating in the touchdown region. However, the touchdownsensor 160 is otherwise exposed to similar conditions as the touchdownsensor 150. The touchdown sensor 160 may thus act as a reference sensorfor the touchdown sensor 150. The touchdown sensor 160 is also desiredto be integrated into the head 100 so that in the absence of touchdown,the touchdown sensor 160 is at or close to the same temperature as thetouchdown sensor 150. A difference between the temperatures detected bythe touchdown sensors 150 and 160 corresponds to contact between thehead 100 and media 60. Stated differently, operation of the touchdownsensors 150 and 160 in a differential mode allows for touchdowndetection for the head 100.

FIG. 2 depicts an exemplary embodiment of a portion of the magnetic head100. For simplicity, components of the head 100 are omitted and themedia 60 is not shown in FIG. 2. In addition, for clarity, FIG. 2 is notdrawn to scale. The magnetic head 100 includes a magnetic readtransducer 110 and write transducer 120. Referring to FIGS. 1-2, thehead 100 may reside on the slider 70 of a disk drive 50. The head 100 isalso described in the context of particular components and layers.However, in some embodiments, such layers may include sub-layer(s). Inaddition, some components may be moved, omitted, or combined with othercomponents.

The read transducer 100 is used in reading from the media 60. The readtransducer 110 includes shields 112 and 116 and sensor 114. The readsensor 114 may include a giant magnetoresistive sensor, such as atunneling magnetoresistive junction. However, in other embodiments, theread sensor 114 may include other and/or additional components.

The write transducer 120 is used in writing to the media 60. The writetransducer 140 includes a first pole 122, auxiliary pole 126, main pole128, write gap 130, coils 124 and 132, and return shield 134. However,in another embodiment, the write transducer 120 other and/or differentcomponents. In addition, one or more portions of the write transducer120 might be omitted in various embodiments. The first pole 122 is shownas separate from shield 116. However, in another embodiment, the secondshield 116 and first pole 122 may be combined.

The head 100 also includes thermal actuator 140 and touchdown sensors150 and 160. The thermal actuator 140 may be used to induce touchdown,as shown in FIG. 1, and otherwise control the spacing of the head 100 tothe media 60. For example, a current may be driven through the thermalactuator 140, which generates heat in the region of the transducers 110and 120. As a result, the transducers 120 and/or 110 may bulge outwardtoward the media 60, as shown in FIG. 1. When enough heat is generatedby the thermal actuator 140, sufficient thermal protrusion occurs forintentional touchdown. This touchdown may be sensed by the touchdownsensors 150 and 160. Once touchdown is detected using the touchdownsensors 150 and 160, the thermal actuator 140 may be driven at a lowerpower in order to ensure that there is a desired space between the head100 and media 60. Thus, use of the thermal actuator 140 allows the flyheight to be selected and controlled.

The touchdown sensors 150 and 160 are used to detect touchdown of thehead 100 on the media 60. In the embodiment shown, the touchdown sensors150 and 160 are temperature sensors. In operation, both touchdownsensors 150 and 160 sense the increase in temperature of the transducer120 due to heat generated by the thermal actuator 140 and othercomponents of the head 100. Both touchdown sensors 150 and 160 may alsobe exposed to similar environmental conditions in the disk drive 50,such as humidity and altitude. Upon touchdown, frictional heating due tocontact between the head 100 and media 60 causes a sharp increase, orjump, in the local temperature of the head 150 in the touchdown region.The temperature increase persists during touchdown. This is in contrastto a transient increase in temperature from transitory contact betweenthe head 100 and media 60, for example due to asperities on the media160. In contrast, the touchdown sensor 160 may not experience thistemperature rise due to touchdown. As a result, there is a temperaturedifference between the touchdown sensor 150 and the touchdown sensor 160that persists during touchdown. Detection of this temperature differenceallows touchdown to be detected.

Operation of the touchdown sensors 150 and 160 may also be explained inconnection with FIG. 3, which depicts the temperatures of the headversus actuator current. The graphs shown in FIG. 3 are for explanatorypurposes only, and are not meant to depict actual temperatures in aparticular head 100. The solid line 200 depicts temperature proximate tothe ABS versus thermal actuator current, while the dashed line 210depicts temperature distal from the ABS versus thermal actuator current.Referring to FIGS. 1-3, a higher current through the thermal actuator140 generates more heat. Therefore, the temperature of the portion ofthe head 100 near the ABS increases with increasing thermal actuatorcurrent. This is shown in the portions of the lines 200 and 210 closerto the temperature axis. An increased temperature also corresponds to alarger thermal protrusion of the head 100 and, therefore, a smallerdistance between the head 100 and media 60. When sufficient current isdriven through the thermal actuator 140, thermal protrusion causescontact, or touchdown, between the media 60 and the head 100. Upontouchdown, frictional heating between the media 60 and head 100 causes asharp increase in the local temperature of the head 100 in the touchdownregion. This sharp increase is shown in the solid line 200 and labeledas corresponding to touchdown. However, to a large extent the sharpincrease in temperature is not experienced distal from the touchdownregion of the ABS. Consequently, dashed line 210 remains substantiallyunchanged. The increase in temperature in the touchdown region persistsduring touchdown as is also shown in FIG. 3. Stated differently thetemperatures for higher thermal actuator currents than touchdown may beviewed as being due to heating from the actuator as well as frictionalheating due to touchdown. This jump in temperature depicted by the solidline 200 may be sensed by the touchdown sensor 150. However, thetouchdown sensor 160 senses a temperature analogous to the temperaturedepicted by the dashed line 210. Because different temperatures aresensed, the output signals of the touchdown sensors 150 and 160 differ.Subtracting the signal (or temperature) of the sensor 160 from thesignal (or temperature) of the sensor 150 results in a smallerdifference signal (or temperature difference). If this difference signal(or temperature difference) meets or exceeds a threshold, then touchdownmay be determined to have occurred.

In the embodiment shown in FIGS. 1-2, the touchdown sensor 150 isexposed to the air-bearing surface (ABS). In another embodiment, thetouchdown sensor 150 may be recessed from the ABS. The touchdown sensor150 is, however, desired to be sufficiently close to the ABS to detectlocal temperature changes due to touchdown. For example, in oneembodiment, the touchdown sensor 150 may be not more than ten to onehundred nanometers from the ABS. in another embodiment, the touchdownsensor 150 may be further from the ABS, for example up to one micronfrom the ABS. In contrast, the touchdown sensor 160 is distal from theABS and thus does not detect local temperature changes due to touchdown.Other than touchdown, the touchdown sensors 150 and 160 are also desiredto be exposed to substantially the same environment, including heat fromthe thermal actuator 140, as the transducers 110 and 120.

The touchdown sensors 150 and 160 are also desired to detect smalltemperature changes, be small in size, unaffected by magnetic fieldsgenerated during operation of the head 100, and not to adversely affectthe read and write operations of the head 100. The touchdown sensors 150and 160 are desired to be substantially unaffected by magnetic fieldsgenerated by the head 100 and media 60, allowing the touchdown sensors150 and 160 to function as desired within the head 100. Alternatively,the effect of magnetic fields due to the head 100 and/or media 60 maycause well known and repeatable changes in the behavior of the touchdownsensors 150 and 160 that can be accounted for. Further, the touchdownsensors 150 and 160 should leave operation of the head 100 substantiallyunaffected.

Although the temperature change in the region of the touchdown sensor150 may persist during touchdown, the temperature change may be small.In addition, the difference between temperatures at the touchdownsensors 150 and 160 may also be small. Consequently, the touchdownsensors 150 and 160 may be capable of detecting a temperature change assmall as 0.1 degree Celsius. In some embodiments, the each touchdownsensor 150 and 160 may be capable of detecting smaller temperaturechanges. For example, in some embodiments, the touchdown sensor 150 andthe touchdown sensor 160 may detect temperature changes of 0.01 degreeCelsius. The touchdown sensor 150 may detect such changes that last foron the order of tens of microseconds or more.

In order to be integrated into the head 100, the touchdown sensors 150and 160 are desired to be relatively small in size. In one embodiment,each touchdown sensor 150 and 160 has a depth, d, that extendsapproximately one micron perpendicular to the ABS (right to left in FIG.2) and one micron along the ABS (perpendicular to the plane of the pagein FIG. 2). However, in other embodiments, the touchdown sensors 150 and160 may have other dimensions. For example, the touchdown sensor 150and/or 160 might be 5 μm×5 μm in the directions discussed above. Inother embodiments, the touchdown sensor 150 and/or 160 may be larger,particularly in a single dimension. For example, in one embodiment, thetouchdown sensor 150 and/or 160 may be elongated to extend fiftymicrometers perpendicular to the ABS and one to five microns along theABS. The thickness, t, of the touchdown sensor 150 and/or 160 is desiredto be small, for example five hundred nanometers or less. In one suchembodiment, t is not more than three hundred nanometers. In oneembodiment, t is two hundred fifty nanometers. Although shown as havingthe same geometry, in another embodiment, the touchdown sensors 150 and160 may have differing geometries, sensitivities, and/or othercharacteristics.

In addition to the above features, each touchdown sensor 150 and 160 mayhave a negative thermal coefficient of resistivity. Thus, as thetouchdown sensor 150 and/or 160 increases in temperature, its resistancedecreases. As a result, the current through the touchdown sensor 150and/or 160 would be concentrated in the hottest portion of the touchdownsensor 150 and/or 160, respectively. Consequently, the sensitivity ofthe touchdown sensor 150 and/or 160 in detecting a positive temperaturechange and, therefore, touchdown, may be increased. However, in anotherembodiment, a touchdown sensor 150 and/or a touchdown sensor 160 havinga positive thermal coefficient of resistivity may be used.

Use of the touchdown sensors 150 and 160 allows for straightforwarddetection of touchdown through the detection of an increase intemperature. Improved detection of touchdown may be used in initialdrive calibration, to provide a common touchdown detection techniqueapplicable from test to product facilitating manufacturing, for routinechecks and adjustments of dynamic fly height setting during operation ofdrive and to detect at inception problems from unintentional touchdownduring drive operation. Improved touchdown detection may enhancecalibration and adjustment of the drive 50. For example, betterdetermination of the location of the media 60 through touchdown mayenhance the ability of the disk drive 50 to fly the head 100 at asmaller controlled spacing from the media 60. Performance of the diskdrive 50 may thus be improved. In addition, a lower fly height may allowthe disk drive 50 to be used at higher storage densities. Further, yieldfor the disk drives may be improved. Similarly, detection ofunintentional touchdown may allow for adjustment of the fly height andmay thus enhance product reliability. For example, changes in operatingenvironment and contamination of the head 100 may be accounted for. Inaddition, with appropriate selection of the touchdown sensors 150 and160, manufacturing of the head 100 including the touchdown sensors 150and 160 as well as modifications to existing circuitry to operate thetouchdown sensors 150 and 160 may be relatively simple. In someembodiments, the function of the touchdown sensors 150 and 160 may beextended to detect temperature increases as the distance between themedia 60 and head 100 decreases. In such an embodiment, the touchdownsensors 150 and 160 may be extended for use in a determination of theproximity of the head 100 to the media 60. Although use of the touchdownsensors 150 and 160 may require inclusion of an additional pad, thetemperature difference, rather than absolute temperature may be measuredfor touchdown detection. Because the temperature difference is smallerin magnitude than the absolute temperature, detection may be furtherfacilitated. For example, more accurate touchdown detection may bepossible and simpler circuitry may be used.

FIGS. 4-5 depict an exemplary embodiment of a touchdown sensor 150′ or160′. The touchdown sensor 150′/160′ may be used for the touchdownsensor 150 or 160 depicted in FIGS. 1-2. Referring back to FIGS. 4-5, inaddition to the actual sensor 150′/160′, contacts 152 and 154 are alsoshown. The contacts 152 and 154 may be metallic, for example composed ofCr. The contacts 152 and 154 may be used to drive current through thesensor 150′/160′, as well as read the resistance and thus temperaturefrom the sensor 150′/160′.

In one embodiment, the sensor 150′/160′ includes an amorphoussemiconductor, such as one or more of amorphous Ge, amorphous Si,amorphous GeSi, and amorphous GeSiO. Such materials have hightemperature sensitivity, allowing detection of temperature changes of0.1 degree or less. Further, such materials provide this temperaturesensitivity at a relatively small size. For example, sensor 150′/160′having width, w, and depth, d, on the order of a few microns or less maybe fabricated. In the embodiment shown in FIG. 5, the width, w, isparallel to the ABS, while the depth, d, is perpendicular to the ABS. Insome embodiments, the touchdown sensor 150′/160′ may be substantiallysquare, with both w and d on the order of five microns or less. Forexample, w and d may each be one micron. In another embodiment, thedimension w or d may be elongated, for example up to fifty microns. Inaddition, the thickness of the sensor 150′/160′ may be small when usingsuch amorphous semiconductors. In one embodiment, the thickness, t, maybe not more than three hundred nanometers. In another embodiment, t maybe not more than two hundred and fifty nanometers. The total height ofthe sensor 150′/160′ and contacts 152 and 154, h, may be on the order offive hundred nanometers or less. In one such embodiment, h is not morethan four hundred fifty nanometers. Thus, sensor 150′/160′ that aresmall in size may be fabricated. Such amorphous semiconductors may alsohave a negative temperature coefficient of resistivity. As a result, theresistance of the sensor 150′/160′ may decline as its temperatureincreases. Current is thus concentrated on the hottest portion of thesensor 150′/160′, which may increase the sensitivity of the sensor150/160′, respectively'. In addition, use of amorphous semiconductorsfor the sensor 150′/160′ allows the sensor to be fabricated using knownphotolithographic and similar techniques. However, in anotherembodiment, the sensor 150′/160′ may include another material, such as atemperature sensitive metal. Further, in another embodiment, theconfiguration of the sensor 150′/160′ and contacts 152 and 154 may bedifferent. In one such embodiment, the contacts 152 and 154 may residein substantially the same plane. In such an embodiment, the currentwould be driven through the sensor 150′/160′ in this plane.

The sensor 150′/160′ may thus be used in the head 100 for detectingtouchdown. Use of the sensor 150′/160′ may provide improved detection oftouchdown. As a result, operation, reliability and manufacturing yieldof the disk drives 50 may be improved.

FIG. 6 depicts a block diagram an exemplary embodiment of a system fordetecting touchdown including a touchdown sensors 150″ and 160″ andtouchdown sensor control circuitry 170. The touchdown sensors 150″ and160″ are analogous to the touchdown sensors 150150′ and 160/160′,respectively. The touchdown sensors 150″ and 160″ may thus be integratedin the head 100 and have the properties described above. Components ofthe control circuitry 170 may be specially included in the disk drive 50or may also be used for other purposes such as read or write operations.

The control circuitry 170 includes current/driver 172, signal receiver174, differential circuitry 176, and threshold setting block 178. Notethat the components 172, 174, 176, and 178 may include multiplefunctions and thus may have multiple sub-components. Such sub-componentsmight be split into separate components. The current/driver 172 drivesthe touchdown sensors 150″ and 160″. In the embodiment shown, thecurrent/driver 172 provides a current to the touchdown sensors 150″ and160″. In another embodiment, the current/driver 172 might provide avoltage or otherwise drive the touchdown sensors 150″ and 160″. Inanother embodiment, separate current drivers may be used for thetouchdown sensors 150″ and 160″. The signal receiver/preamp 174 receivesoutput signals from the touchdown sensors 150″ and 160″. In oneembodiment the signal receiver/preamp 174 may include the preamplifierfor the read sensor 114 or other circuitry used by the head 100. Inaddition, separate signal receivers/preamps may be used for eachtouchdown sensor 150″ and 160″. In another embodiment, differentialvoltage or analogous differential signals may be read from the touchdownsensors 150″ and 160″. The differential circuitry block 176 may processthe signals from the touchdown sensors 150″ and 160″. For example, thesignals from the touchdown sensors 150″ and 160″ may be subtracted andthe difference compared to a threshold. The threshold may be providedvia threshold setting block, 178. Thus, the block 176 may determinewhether the signal from the touchdown sensor 150″ indicates asufficiently large change in temperature for a sufficient interval fortouchdown to be detected. Thus, through the use of the touchdown sensors150″ and 160″and control circuitry 170, touchdown may be detected.

FIG. 6 also depicts thermal actuator 140′ and thermal actuatorcontroller/driver 142. The thermal actuator controller/driver 142 mayalso include multiple subcomponents. The thermal actuatorcontroller/driver 142 receives the signal from the touchdown sensorcontrol circuitry 170 and determines the desired level of current to bedriven through the thermal actuator 140′. The thermal actuatorcontroller/driver 142 also provides the desired level of current to thethermal actuator 140′. The thermal actuator 140′ corresponds to thethermal actuator 140 in the head 100. Thus, the thermal actuator 140′heats the head 100 a desired amount.

In operation, when intentional touchdown is to be detected, the thermalactuator 140′ is driven at increasing current. The touchdown sensor 150″detects a sharp increase in temperature when touchdown occurs. However,the touchdown sensor 160″ detects a temperature that does not undergo asimilar jump upon touchdown. Based on the difference in the outputsignals from the touchdown sensors 150″ and 160″, the control circuitry170 determines that touchdown has occurred. This may be achieved bycomparing the difference in the sensed temperatures to a threshold.Temperature differences at or greater than the threshold may beconsidered to correspond to touchdown. The thermal actuatorcontroller/driver 142 may then react, for example by reducing thecurrent to the thermal actuator 140′. The thermal actuator 140′ isdriven at a lower power, and the heat in the head 100 reduced.Consequently, the head 100 may fly at a small, controlled spacing abovethe media.

Using the system including touchdown sensor 50″ and control circuitry170 detection of touchdown may be improved. As a result, operation,reliability and manufacturing yield of the disk drives 50 may beimproved.

FIG. 7 depicts an exemplary embodiment of a method 300 for detectingtouchdown using a touchdown sensor integrated into a head. The method300 is used in connection with the head 100, touchdown sensor150/150′/150″, and touchdown sensors 160/160′/160″. Further, althoughdepicted as a flow of single steps, the steps of the method 300 may beperformed in parallel and/or continuously.

The temperature of the head 100 in the touchdown region of the ABS ismonitored, via step 302. Step 302 may be performed continuously duringcalibration or operation of the disk drive 50 using the touchdown sensor150/150′/150″. The temperature of the head 100 in the region distal fromthe touchdown region of the ABS is monitored, via step 304. Step 304 maybe performed continuously during calibration or operation of the diskdrive 50 using the touchdown sensor 160/160′/160″. Alternatively steps302 and 304 could be replaced by monitoring of the temperaturedifference between the touchdown region and a portion of the head 100distal from the ABS. It is determined whether touchdown has occurredbased on the difference between the temperatures monitored in steps 302and 304, via step 306.

FIG. 8 depicts another exemplary embodiment of a method 310 fordetecting touchdown using touchdown sensors integrated into a head. Themethod 310 is used in connection with the head 100, touchdown sensor150/150′/150″, and touchdown sensor 160/160′/160″. Consequently, themethod 310 is described in connection with the head 100 and touchdownsensors 150/150′/150″ and 160/160′/160″. Further, although depicted as aflow of single steps, the steps of the method 310 may be performed inparallel and/or continuously. The method 310 may also be viewed as anembodiment of the method 300.

A first temperature of the head 100 is detected using the temperaturesensor 150/150′/150″ integrated in the head 100, via step 312. Thetemperature sensor is proximate to the ABS and capable of detecting atemperature change of 0.1 degree. A second temperature is also detectedusing the temperature sensor 160/160′/160″, via step 314. The secondtemperature is thus monitored distal from the ABS. Steps 312 and 314 maybe performed multiple times in order to obtain trends in the temperatureof the head 100. In addition, although described as temperaturedetection, steps 312 and 314 may simply include the temperature sensors150/150′/150″ and 160/160′/160″ providing to the circuitry 170 signalscorresponding to temperatures proximate to and distal from the ABS.Alternatively steps 312 and 314 may be replaced by monitoring thedifference between the temperatures sensed by the temperature sensor150/150′/150″ and the sensor 160/160′/160″.

A difference between the first temperature and the second temperature iscalculated, via step 316. In one embodiment, step 316 is performed bythe component 176. Step 316 may include determining an actualtemperature difference, or simply determining the difference in signalsfrom the temperatures sensor 150/150′/150″. Note that if the temperaturedifference is monitored in lieu of steps 312 and 314, step 316 may beomitted.

Touchdown is determined to have occurred if the difference intemperatures or a change in the rate of change in temperature withactuator current is at least a threshold, via step 318. In oneembodiment, step 318 detects occurrence of a touchdown if the differenceor the change in the rate of change in temperature is greater than thethreshold. In one such embodiment, touchdown is determined to havehappened if the difference or the change in the rate of change intemperature meets or exceeds the threshold for a certain amount of time.Thus, touchdown may be detected.

Using the method 300 and/or 310 the temperature sensors 150/150′/150″and 160/160′/160″ may be used to detect touchdown. As a result,detection of touchdown may be improved. Operation, reliability andmanufacturing yield of the disk drives 50 may thus be improved.

1. A disk drive comprising: a slider; a head residing on the slider andhaving an air-bearing surface (ABS), a portion of the ABS contacting amedium during a touchdown, the head further including a plurality oftouchdown sensors, a first touchdown sensor proximate to the ABS, asecond sensor distal from the ABS, the plurality of touchdown sensorscapable of detecting a temperature change of 0.1 degree Celsius.
 2. Thedisk drive of claim 1 wherein the first touchdown sensor is configuredto sense a first temperature and the second touchdown sensor isconfigured to sense a second temperature, the disk drive furthercomprising: differential circuitry coupled with the first touchdownsensor and the second touchdown sensor configured to determine adifference between the first temperature and the second temperature. 3.The disk drive of claim 2 further comprising touchdown sensor controlcircuitry coupled with the plurality of touchdown sensors and includingthe differential circuitry, the touchdown sensor control circuitry fordriving at least one current through the plurality of touchdown sensorsand converting a signal from the differential circuitry to an indicationof whether the touchdown has occurred.
 4. The disk drive of claim 1 thefirst touchdown sensor is configured to sense a first temperature andthe second touchdown sensor is configured to sense a second temperature,the disk drive further comprising: further comprising differentialcircuitry for monitoring a difference between the first temperature andthe second temperature.
 5. The disk drive of claim 1 wherein at leastone of the first touchdown sensor and the second touchdown sensor is athermistor.
 6. The disk drive of claim 5 wherein at least one of thefirst touchdown sensor and the second touchdown sensor includes a metal.7. The disk drive of claim 5 wherein the at least one of the first andsecond touchdown sensors includes a first metal layer, and a secondmetal layer, a portion of the at least one amorphous semiconductorresiding between a portion of the first metal layer and a portion of thesecond metal layer.
 8. The disk drive of claim 1 wherein at least one ofthe first touchdown sensor and the second touchdown sensor includes atleast one amorphous semiconductor.
 9. The disk drive of claim 8 whereinthe at least one amorphous semiconductor includes at least one of Ge,Si, GeSi, and GeSiO.
 10. The disk drive of claim 1 wherein each of theplurality of touchdown sensors is capable of detecting the temperaturechange of 0.01 degree Celsius.
 11. The disk drive of claim 1 whereineach of the plurality of touchdown sensors has a lateral dimension ofnot more than fifty microns.
 12. The disk drive of claim 11 wherein thelateral dimension is not more than one micron.
 13. The disk drive ofclaim 1 wherein each of the plurality of touchdown sensors has athickness of not more than five hundred nanometers.
 14. The disk driveof claim 1 wherein each of the plurality of touchdown sensors has anegative thermal coefficient of resistivity.
 15. The disk drive of claim1 wherein at least one of the first touchdown sensor and the secondtouchdown sensor has a positive thermal coefficient of resistivity. 16.A disk drive comprising: a slider; a head residing on the slider andhaving an air-bearing surface (ABS), a portion of the ABS contacting amedium during a touchdown, the head further including a first touchdownsensor proximate to the ABS and a second sensor distal from the ABS, thefirst touchdown sensor and the second touchdown sensor including atleast one of amorphous Ge, Si, GeSi, and GeSiO, each of the first andsecond touchdown sensors further including a first metal layer, and asecond metal layer, a portion of the at least one amorphoussemiconductor residing between a portion of the first metal layer and aportion of the second metal layer, each of the first touchdown sensorand the second touchdown sensor capable of detecting a temperaturechange of 0.1 degree Celsius and having a lateral dimension of not morethan one micron; and differential circuitry coupled with the firsttouchdown sensor and the second touchdown sensor configured to determinea difference between the first temperature and the second temperature.17. A method for detecting a touchdown between a head having anair-bearing surface (ABS) and a disk in a disk drive, the methodcomprising: determining a first temperature of a first touchdown sensorintegrated in the head, the first touchdown sensor being proximate tothe ABS and capable of detecting a temperature change of 0.1 degreeCelsius; determining a second temperature of a second touchdown sensorintegrated in the head, the second touchdown sensor being distal fromthe ABS and capable of detecting the temperature change; calculating adifference between the first temperature and the second temperature; anddetecting the touchdown based on the difference.
 18. The method of claim17 wherein the step of detecting further includes: detecting thetouchdown if the difference is at least a threshold.
 19. The method ofclaim 17 wherein the step of detecting further includes: detecting thetouchdown if a change in a rate of change of temperature is at least athreshold.
 20. The method of claim 17 wherein at least one of the firsttouchdown sensor and the second touchdown sensor is a thermistor. 21.The method of claim 17 wherein at least one of the first touchdownsensor and the second touchdown sensor includes at least one amorphoussemiconductor.
 22. The method of claim 21 wherein the at least oneamorphous semiconductor includes at least one of Ge, Si, GeSi, andGeSiO.
 23. The method of claim 21 wherein the at least one of the firstand second touchdown sensors includes a first metal layer, and a secondmetal layer, a portion of the at least one amorphous semiconductorresiding between a portion of the first metal layer and a portion of thesecond metal layer.
 24. The method of claim 17 wherein at least one ofthe first touchdown sensor and the second touchdown sensor includes atemperature sensitive metal.
 25. The method of claim 17 wherein thefirst touchdown sensor has a first negative thermal coefficient ofresistivity and the second touchdown sensor has a second negativethermal coefficient of resistivity.